1. Field of the Invention
The present invention relates to energy efficient electromagnetic circuits. The present invention relates specifically to an electromagnetic latching relay circuit.
2. Description of the Prior Art
Electromagnetic circuits are used to accomplish a wide variety of tasks. Typically such circuits utilize permanent magnets and/or electromagnets to accomplish the desired task. U.S. Pat. No. 3,914,723 to Goodbar, for example, discloses a magnetic latching relay using a permanent magnet and an electromagnet. The electromagnet, when activated, causes the permanent magnet to move, opening or closing a pair of contacts. Similar circuits are disclosed in U.S. Pat. No. 4,620,173 to O'Brien and U.S. Pat. No. 4,998,082 to Duimstra. Each of these use electric coils to create magnetic fields which move permanent magnets or electromagnets, thereby accomplishing some task. In each of the circuits disclosed, the electric coil is activated and consumes energy for some discrete period of time. The period may be arbitrarily longer than that necessary to accomplish the desired result, as when the coil is activated until the relay is switched, then deactivated at some arbitrary later time. The period may also correlate to the length of time the desired result is to be maintained, as when the coil is kept activated to "latch" the relay. In either case the electric coil consumes energy while it is activated. It is desirable to avoid this power consumption.
It is also known that certain materials, including Alnico alloys, may be readily induced with a "residual" magnetism. When exposed to a magnetic field of sufficient strength, these materials become magnetic and remain magnetic when the inducing magnetic field is removed. The polarity of the residual magnetism corresponds to the polarity of the inducing magnetic field, making these materials selectively magnetizable.